Posterior atlantoaxial fixation of osteoporotic odontoid fracture: biomechanical analysis of the Magerl versus harms techniques in a cadaver model.

BACKGROUND CONTEXT: Odontoid fractures are among the most common cervical spine fractures in the elderly and are associated with increased morbidity and mortality. Clinical evidence suggests improved survival and quality of life after operative intervention compared to nonoperative treatment. PURPOSE: This study seeks to examine the stability of an osteoporotic Type II odontoid fracture following posterior atlantoaxial fixation with either the Magerl transarticular fixation technique or the Harms C1 lateral mass screws C2 pedicle screw rod fixation. STUDY DESIGN: Biomechanical cadaveric study. METHODS: Eighteen cadaveric specimens extending from the cephalus to C7 were used in this study. Reflective marker arrays were attached to C1 and C2 and a single marker on the dens to measure movement of each during loading with C2-C3 and occiput-C1 being allowed to move freely. A biomechanical testing protocol imparted moments in flexion-extension, axial rotation, and lateral bending while a motion capture system recorded the motions of C1, C2, and the dens. The spines were instrumented with either the Harms fixation (n=9) or Magerl fixation (n=9) techniques, and a simulated Type II odontoid fracture was created. Motions of each instrumented spine were recorded for all moments, and then again after the instrumentation was removed to model the injured, non-instrumented state. RESULTS: Both Harms and Magerl posterior C1-C2 fixation allowed for C1, C2, and the dens to move as a relative unit. Without fixation the dens motion was coupled with C1. No significant differences were found in X, Y, Z translation motion of the dens, C1 or C2 during neutral zone motions between the Magerl and Harms fixation techniques. There were no significant differences found in Euler angle motion between the two techniques in either flexion-extension, axial rotation, or lateral bending motion. CONCLUSIONS: Our findings suggest that both Harms and Magerl fixation can significantly reduce dens motion in Type II odontoid fractures in an osteoporotic cadaveric bone model. CLINICAL SIGNIFICANCE: Both Harms and Magerl posterior atlantoaxial fixation techniques allowed for C1, C2, and the dens to move as a relative unit following odontoid fracture, establishing more anatomic stability to the upper cervical spine.

Radiographic Anatomy of the Lateral Ankle Ligament Complex: A Cadaveric Study.

BACKGROUND: When lateral ankle sprains progress into chronic lateral ankle instability (CLAI), restoring precise anatomic relationships of the lateral ankle ligament complex (LALC) surgically is complex. This study quantifies the radiographic relationships between the anterior talofibular ligament (ATFL), calcaneofibular ligament (CFL), and prominent osseous landmarks visible under fluoroscopy to assist in perioperative practices for minimally invasive surgery for CLAI. METHODS: Ten fresh frozen ankle specimens were dissected to expose the LALC and prepared by threading a radiopaque filament through the ligamentous footprints of the ATFL and CFL. Fluoroscopic images were digitally analyzed to define dimensional characteristics of the ATFL and CFL. Directional measurements of the ligamentous footprints relative to the lateral process of the talus and the apex of the posterior facet of the calcaneus were calculated. RESULTS: Dimensional measurements of the ATFL were a mean length of 9.3 mm, fibular footprint of 9.4 mm, and talar footprint of 9.1 mm. Dimensional measurements of the CFL were a mean length of 19.4 mm, fibular footprint of 8.2 mm, and calcaneal footprint of 7.3 mm. From the radiographic apparent tip of the lateral process of the talus, the fibular attachment of the ATFL was found 13.3 mm superior and 4.4 mm posterior, whereas the talar attachment was found 11.5 mm superior and 4.8 mm anterior. From the radiographic apparent posterior apex of the posterior facet of the calcaneus, the fibular attachment of the CFL was found 0.2 mm inferior and 6.8 mm anterior, whereas the calcaneal attachment was found 14.3 mm inferior and 5.9 mm posterior. CONCLUSION: The ATFL and CFL were radiographically analyzed using radiopaque filaments to outline the ligamentous footprints in their native locations. These ligaments were also localized with reference to 2 prominent osseous landmarks. These findings may assist in perioperative practices for keyhole incision placement and arthroscopic guidance. Perfect lateral ankle joint imaging with talar domes superimposed is required to be able to do this. CLINICAL RELEVANCE: Radiographic evaluation of the ATFL and CFL with reference to prominent osseous landmarks identified under fluoroscopy may assist in perioperative practices for minimally invasive surgery to address CLAI for keyhole incision placement and arthroscopic guidance.

Characterization of regional variation of bone mineral density in the geriatric human cervical spine by quantitative computed tomography.

BACKGROUND: Odontoid process fractures are among the most common in elderly cervical spines. Their treatment often requires fixation, which may include use of implants anteriorly or posteriorly. Bone density can significantly affect the outcomes of these procedures. Currently, little is known about bone mineral density (BMD) distributions within cervical spine in elderly. This study documented BMD distribution across various anatomical regions of elderly cervical vertebrae. METHODS AND FINDINGS: Twenty-three human cadaveric C1-C5 spine segments (14 males and 9 female, 74±9.3 y.o.) were imaged via quantitative CT-scan. Using an established experimental protocol, the three-dimensional shapes of the vertebrae were reconstructed from CT images and partitioned in bone regions (4 regions for C1, 14 regions for C2 and 12 regions for C3-5). The BMD was calculated from the Hounsfield units via calibration phantom. For each vertebral level, effects of gender and anatomical bone region on BMD distribution were investigated via pertinent statistical tools. Data trends suggested that BMD was higher in female vertebrae when compared to male ones. In C1, the highest BMD was found in the posterior portion of the bone. In C2, BMD at the dens was the highest, followed by lamina and spinous process, and the posterior aspect of the vertebral body. In C3-5, lateral masses, lamina, and spinous processes were characterized by the largest values of BMD, followed by the posterior vertebral body. CONCLUSIONS: The higher BMD values characterizing the posterior aspects of vertebrae suggest that, in the elderly, posterior surgical approaches may offer a better fixation quality.

Relationship to drill bit diameter and residual fracture resistance of the distal tibia.

BACKGROUND: The etiology of bone refractures after screw removal can be attributed to residual drill hole defects. This biomechanical study compared the torsional strength of bones containing various sized cortical drill defects in a tibia model. METHODS: Bicortical drill hole defects of 3 mm, 4 mm, and 5 mm diameters were tested in 26 composite tibias versus intact controls without a drill defect. Each tibia was secured in alignment with the rotational axis of a materials testing system and the proximal end rotated internally at a rate of 1 deg./s until mechanical failure. FINDINGS: All defect test groups were significantly lower (P < 0.01) in torque-to-failure than the intact group (82.80 ± 3.70 Nm). The 4 mm drill hole group was characterized by a significantly lower (P = 0.021) torque-to-failure (51.00 ± 3.27 Nm) when compared to the 3 mm drill hole (59.00 ± 5.48 Nm) group, but not different than the 5 mm hole group (55.71 ± 5.71 Nm). All bones failed through spiral fractures, bones with defects also exhibited posterior butterfly fragments. INTERPRETATION: All the tested drill hole sizes in this study significantly reduced the torque-to-failure from intact by a range of 28.4% to 38.4%, in agreement with previous similar studies. The 5 mm drill hole represented a 22.7% diameter defect, the 4 mm drill hole a 18.2% diameter defect, and the 3 mm drill hole a 13.6% diameter defect. Clinicians should be cognizant of this diminution of long bone strength after a residual bone defect in their creation and management of patient rehabilitation programs.

How Does Tibial Pin Placement in Navigated Total Knee Arthroplasty Affect the Torsional Strength of the Tibia?

INTRODUCTION: Surgical navigation technology has recently become more prevalent for total knee arthroplasty. Surgical navigation typically requires pin placement in the proximal tibia diaphysis to stabilize the bone-tracking hardware, and there have been several recent reports of fractures through these residual navigation pin holes. The objective of this biomechanical study was to determine whether a difference exists in the torsional bone strength of a 5-mm navigation pin hole drilled at a single location in three different orientations: unicortical, bicortical, and transcortical. METHODS: Biomechanical composite sawbone tibias were used to test four conditions: the intact condition with no holes, a unicortical hole, a bicortical hole, and a transcortical hole through the proximal diaphysis. Seven specimens from each group were tested in external rotation to failure at 1 deg/sec. Torque-to-failure, absorbed energy-to-failure, and rotational angle-to-failure were statistically compared across the four groups. RESULTS: All specimens failed proximally by spiral oblique fractures. No statistical differences were found between unicortical and bicortical groups in torque-to-failure, energy-to-failure, and angle-to-failure. However, both unicortical and bicortical groups were markedly lower in all measures than the intact group. The transcortical group was markedly lower in all measures than the intact group and both unicortical and bicortical groups. DISCUSSION: An appropriately placed navigation residual pin hole, either unicortical or bicortical, markedly decreases the torque-to-failure, energy-to-failure, and angle-to-failure of the tibia compared with the intact condition in a synthetic sawbones model. No notable difference was detected between the unicortical and bicortical holes; however, an errant transcortical residual navigation pin hole markedly decreases all measures compared with an appropriately placed unicortical or bicortical hole.

Quadruple Versus Double Flexible Intramedullary Nails to Treat Pediatric Distal-third Tibial Shaft Fractures: A Biomechanical Comparison.

BACKGROUND: The vast majority of pediatric distal-third tibial shaft fractures can be treated with closed reduction and casting. If conservative measures fail, then these fractures are usually treated with 2 antegrade flexible intramedullary nails. A postoperative cast is usually applied because of the tenuous fixation of the 2 nails. Recent studies have described the use of 4 nails to increase the stability of the fixation, a technique that may preclude the need for postoperative casting. The purpose of this biomechanical study is to quantify the relative increase in stiffness and load to failure when using 4 versus 2 nails to surgically stabilize these fractures. METHODS: Short, oblique osteotomies were created in the distal third of small fourth-generation tibial sawbones and stabilized with 2 (double) or 4 (quadruple) flexible intramedullary nails. After pilot testing, 5 models per fixation method were tested cyclically in axial compression, torsion, and 4-point bending in valgus and recurvatum. At the end of the study, each model was loaded to failure in valgus. Stiffness values were calculated, and yield points were recorded. The data were compared using Student's t tests. Results are presented as mean±SD. The level of significance was set at P≤0.05. RESULTS: Stiffness in valgus 4-point bending was 624±231 and 336±162 N/mm in the quadruple-nail and double-nail groups, respectively (P=0.04). There were no statistically significant differences in any other mode of testing. CONCLUSIONS: The quadruple-nail construct was almost 2 times as stiff as the double-nail construct in resisting valgus deformation. This provides biomechanical support for a previously published study describing the clinical success of this fixation construct.

Cortical suture button fixation vs. bicortical screw fixation in the Latarjet procedure: a biomechanical comparison.

BACKGROUND: The Latarjet procedure traditionally has been performed with 2 screws in an open manner. Recently, cortical suture button fixation for coracoid transfer has been used in hopes of mitigating complications seen with screw placement. The aim of this study was to evaluate a cortical suture button and technique currently available in the United States compared with screw fixation in the Latarjet procedure in a cadaveric model. METHODS: We randomly assigned 9 matched pairs of fresh-frozen cadaveric shoulders (N = 18) to undergo the Latarjet procedure with either screw fixation or cortical suture button fixation. After fixation, all shoulders underwent biomechanical testing with direct loading on the graft vas a material testing system. Cyclic testing was performed for 100 cycles to determine axial displacement with time; each graft was then monotonically loaded to failure. RESULTS: The maximum cycle displacement was significantly less for screw fixation vs. cortical suture button fixation (3.1 ± 1.3 mm vs. 8.9 ± 2.1 mm, P < .0001). The total load at failure was 481.1 ± 88.8 N for screws and 175.5 ± 95.8 N for cortical suture buttons (P < .0001). Bony damage to the surrounding anatomy was more extensive at failure in the screw-fixation group. CONCLUSION: At time zero, the cortical button fixation and technique did not resist direct loads to the graft as much as traditional screw fixation, although bony damage to the surrounding anatomy was more extensive in screw fixation than button fixation. In the event of unanticipated loading, this could place a patient at higher risk of graft migration, which could lead to unintended early outcomes. These results support the need for implants and techniques specifically tailored to the Latarjet procedure and should bring into question the adoption of a cortical button and technique not specific to the procedure.

Biomechanical Evaluation of Humerus Fracture After Subpectoral Biceps Tenodesis With Interference Screw Versus Unicortical Button.

PURPOSE: To compare the torsional failure strength of the humerus after subpectoral biceps tenodesis with an interference screw versus a unicortical button in a human cadaveric model. METHODS: Thirteen matched pairs of fresh-frozen human cadaveric upper extremities were randomized to receive either 2.6 × 12 mm unicortical button or 6.25-mm interference screw subpectoral biceps tenodesis. After the procedure, the humeri were loaded into a materials testing machine. The humeri were loaded in external rotation with respect to the elbow at 1.0°/s until failure. Rotation angle to failure, failure torque, energy absorbed, and stiffness were compared by paired t-tests with alpha set at 0.05. RESULTS: Humeri that were fixed with unicortical buttons showed statistically significant higher rotation to failure (26.87 ± 5.83 vs 19.04 ± 3.86°, P < .001), failure torque (54.11 ± 22.01 vs 44.95 ± 17.47 Nm, P < .001), and energy absorbed (883.93 ± 582.28 vs 451.40 ± 216.19 Nm-Deg, P = .002) than humeri fixed with interference screws. CONCLUSIONS: In a cadaveric biomechanical model, at time 0, the use of a 2.7 × 12-mm unicortical button fixation in biceps tenodesis resulted in higher loads required to fracture the humerus when compared with a 6.25-mm interference screw fixation in a torsion model. CLINICAL RELEVANCE: This study demonstrates a significant biomechanical difference with regards to fracture of the humerus, between 2 commonly used fixations methods and implant sizes, interference screw, and unicortical button. The results of this study can aid surgeons in implant selection as well as help to improve patient education prior to surgery.

Biomechanical Evaluation of Dual Plate Configurations for Femoral Shaft Fracture Fixation.

AIM: This study aimed at comparing the mechanical properties of conventional and locking dual plates in adjacent and orthogonal orientations for the surgical fixation of transverse femoral shaft fractures. It also assessed the failure mechanics after dual adjacent and orthogonal locking plate removal. METHODS: Thirty-two composite femurs were transversally osteotomized and randomly assigned for fixation with either dual locking or compression plates in an adjacent or orthogonal configuration. Sixteen specimens were preloaded axially to 20 N and single-leg stance loads were simulated. The remaining sixteen constructs were subjected to torsional loads of 10 Nm at a rate of 10 Nm/s in external and internal rotation of the femoral head in relation to the knee. Overall combined rotational stiffness was calculated. Eight different specimens with no osteotomy underwent the same experiments after dual locked plate removal and were tested to failure in combined eccentric axial and torsional modes. Data were statistically processed using a two-tailed t-test and one-way analysis of variance for the comparison of means between two or more groups, respectively. RESULTS: Orthogonal constructs were statistically stiffer in axial loading compared to their adjacent counterparts in both conventional and locking configurations (p<0.001). Dual locking plates provided higher torsional stiffness than conventional ones within each plate orientation (p<0.01). Neither axial/torsional strength nor failure loads differed between constructs that had adjacent or orthogonal dual locking plates instrumented and then removed (p>0.05). CONCLUSIONS: In both orthogonal and adjacent orientations, double locking plates provide higher stability than their dual conventional counterparts. Orthogonal dual plate configuration is more stable and biomechanically superior to dual adjacent plating for constructs fixed with either standard compression or locking plates.

The Impact of Eccentric Diaphyseal Plate and Screw Placement on the Risk of Peri-Implant Fracture.

BACKGROUND: The objective of this study was to determine the impact of the type and orientation of peripheral screw placement in an eccentrically positioned locking plate on the structural integrity of the plate-diaphyseal bone interface. We hypothesized that central placement of the screw at the end of the plate in this setting is more important than screw type (locking versus nonlocking) to limiting the risk of subsequent fracture. METHODS: Twenty osteoporotic fourth-generation composite left humeri were divided into 4 groups and plated with stainless-steel 6-hole locking plates and 4.5-mm screws. Group 1 (control group) consisted of a centrally positioned plate with a centrally placed non-locking end screw at the sixth, most-proximal hole. Group 2 consisted of an eccentrically positioned plate with a non-locking proximal end screw placed through the center of the bone. Group 3 consisted of an eccentrically positioned plate with a locking proximal end screw placed perpendicular to the plate and eccentrically across the cortex. Group 4 consisted of an eccentrically positioned plate with a non-locking proximal end screw placed perpendicular to the plate and eccentrically across the cortex. Each group was tested with a single load to failure in torsion at a rate of 1°/second. RESULTS: The control group (Group 1) failed at significantly higher peak torque values (51.62 ± 7.35 Nm) than Group 2 (38.98 ± 6.78 Nm; p = 0.006), Group 3 (34.75 ± 1.81 Nm; p < 0.001), and Group 4 (31.55 ± 1.23 Nm; p < 0.001). Failure energy absorbed in Group 1 (2,591.49 ± 819.63 Nm/degree) was significantly higher than Group 3 (1,430.51 ± 449.99 Nm/degree; p = 0.04) and Group 4 (952.49 ± 123.52 Nm/degree; p = 0.004), but not significantly higher than Group 2 (1,847.73 ± 827.35 Nm/degree; p = 0.27). CONCLUSIONS: Eccentrically placed plating of humeral shaft fractures significantly increases the risk of peri-implant fracture compared with a centrally placed plate. Directing the proximal-end screw centrally in an eccentrically placed plate may help to mitigate this risk at the proximal end. CLINICAL RELEVANCE: When possible, care should be taken to place the plate centrally on the bone to avoid increased risk of peri-implant fracture at the proximal plate-bone interface.

Effect of Plate in Close Proximity to Empty External-Fixation Pin Site on Long-Bone Torsional Strength.

Complex tibia fractures are often provisionally stabilized with external fixation prior to definitive fracture fixation. Bicortical defects, such as those left after removal of a fixator pin, can decrease the torsional strength of long bone. Evaluating the effect of subsequent plate fixation in close proximity to a defect on the torsional strength of the tibia is the purpose of this study. Eight groups of 5 fourth-generation left composite tibias were tested to failure in torsion. The experimental plated groups consisted of bicortical defects at 3 cm, 2 cm, and 1 cm distal to the plate end, with 1 plated group without a defect. The control groups consisted of equivalent defects in the same distal longitudinal locations, without plates attached, as well as an unplated group without a defect. There were no statistical differences in torsional stiffness or failure torque between any of the groups. The mode of failure for all specimens with bicortical defects was a spiral fracture that bisected the axis of the defect. Based on the results of this composite tibia study, varying the proximity of a bicortical defect to a plate does not affect the torsional stiffness or torsional failure strength of the bone.

The Effect of Suture Anchor Insertion Angle on Calcaneus Pullout Strength: Challenging the Deadman's Angle.

BACKGROUND: Refractory cases of Achilles tendinopathy amenable to surgery may include reattachment of the tendon using suture anchors. However, there is paucity of information describing the optimal insertion angle to maximize the tendon footprint and anchor stability in the calcaneus. The purpose of this investigation is to compare the fixation strength of suture anchors inserted at 90° and 45° (the Deadman's angle) relative to the primary compressive trabeculae of the calcaneus. METHODS: A total of 12 matched pairs of adult cadaveric calcanei were excised and potted to approximate their alignment in vivo. Each pair was implanted with 5.5-mm bioabsorbable suture anchors placed either perpendicular (90°) or oblique (45°) to the primary compressive trabeculae. A tensile load was applied until failure of anchor fixation. Differences in failure load and stiffness between anchor fixation angles were determined by paired t-tests. RESULTS: No significant differences were detected between perpendicular and oblique suture anchor insertion relative to primary compressive trabeculae in terms of load to failure or stiffness. CONCLUSION: This investigation suggests that the fixation strength of suture anchors inserted perpendicular to the primary compression trabeculae and at the Deadman's angle are possibly comparable. LEVELS OF EVIDENCE: Biomechanical comparison study.

Relationship Between Ulnar Variance, Cortical Bone Density, and Load to Failure in the Distal Radius at the Typical Site of Fracture Initiation.

PURPOSE: Increased ulnar variance has been shown to lead to diminished load borne by the distal radius. The purpose of this study was to determine the correlations among ulnar variance, bone mineral density, and load to failure at the distal radius. METHODS: Posteroanterior radiographs and computed tomographic scans were taken of 12 cadaveric forearms in neutral rotation. Ulnar variance was measured for each wrist by the method of perpendiculars. Measurements of cortical, trabecular, and combined bone density were made at the distal radius. We performed linear regression analysis and correlation analysis to determine the relationship between bone densities and ulnar variance measurements. Next, we loaded the 12 cadaveric radii to failure under axial compression. Linear regression analysis and correlation analysis were then performed to determine the relationship between load to failure and both ulnar variance and cortical density. RESULTS: Increased ulnar variance was significantly correlated with decreased cortical bone density at the distal radius and both were correlated with decreased load to failure. We found no correlation between ulnar variance and trabecular density or combined trabecular and cortical bone density at the distal radius. CONCLUSIONS: Our study found that increased ulnar variance and decreased cortical bone mineral density correlates with decreased load to failure under axial compression. CLINICAL RELEVANCE: Ulnar variance is linked to both bone quality and load to failure at the distal radius.

Biomechanical Comparison of Bicortical, Unicortical, and Unicortical Far-Cortex-Abutting Screw Fixations in Plated Comminuted Midshaft Clavicle Fractures.

PURPOSE: The objective of this study was to assess the biomechanical properties of bicortical locking screws, unicortical locking screws, and unicortical far-cortex-abutting locking screw fixation in a cadaver model of comminuted midshaft clavicle fractures stabilized with a locking plate placed on the superior surface of the clavicle. METHODS: Nine pairs of adult fresh-frozen cadaver clavicles were allocated into 3 groups for either bicortical, unicortical, or unicortical far-cortex-abutting locking plate fixation. After a 1-cm osteotomy to simulate a comminuted fracture and instrumentation with an 8-hole locking plate placed on the superior surface of the clavicle, the specimens were mounted in a custom dual-gimbal fixture in a materials-testing system and tested in axial compression, torsional, and torsional load to failure. RESULTS: Axial stiffness and axial osteotomy site stiffness did not demonstrate differences between constructs. In cyclical torsion, both the bicortical and the unicortical far-cortex-abutting constructs were significantly stiffer than the unicortical construct. For torsional failure stiffness, both the bicortical and the unicortical far-cortex-abutting constructs were significantly stiffer than the unicortical construct. There was no difference between bicortical and unicortical far-cortex-abutting for torsional failure stiffness. The bicortical construct exhibited significantly higher peak failure torque compared with the unicortical construct. CONCLUSIONS: Unicortical far-cortex-abutting locking screw fixation provides comparable mechanical properties under axial and torsional loads to bicortical fixation, without penetrating the far cortex. CLINICAL RELEVANCE: Unicortical far-cortex-abutting locking screw fixation obviates far cortex penetration, and thereby protects nearby anatomical structures, may ease symptomatic implant removal, alleviates refracture risk, and eases conversion to bicortical fixation in the case of revision surgery.

Torsional Failure of Carbon Fiber Composite Plates Versus Stainless Steel Plates for Comminuted Distal Fibula Fractures.

BACKGROUND: Carbon fiber composite implants are gaining popularity in orthopedics, but with few independent studies of their failure characteristics under supra-physiologic loads. The objective of this cadaveric study was to compare torsional failure properties of bridge plating a comminuted distal fibula fracture with carbon fiber polyetheretherketone (PEEK) composite and stainless steel one-third tubular plates. METHODS: Comminuted fractures were simulated in 12 matched pairs of fresh-frozen human fibulas with 2-mm osteotomies located 3 cm proximal to the tibiotalar joint. Each fibula pair was randomized for fixation and implanted with carbon fiber and stainless steel 5-hole one-third tubular plates. The constructs were loaded in external rotation at a rate of 1-degree/sec until failure with a materials testing system. Torsional stiffness and mode of failure, as well as displacement, torque, and energy absorption for the first instance of failure and peak failure, were determined. Statistical analysis was performed with paired t tests and chi-square. RESULTS: There were no significant differences among the 12 pairs for torsional stiffness, first failure torque, peak failure displacement, peak failure torque, or peak failure energy. Stainless steel plates exhibited significantly higher displacement (P < .001) and energy absorption (P = .001) at the first indication of failure than the carbon fiber plates. Stainless steel plates permanently deformed significantly more often than the carbon fiber plates (P = .035). Carbon fiber plates exhibited no plastic deformation with delamination of the composite, and brittle catastrophic failure in 1 specimen. CONCLUSIONS: In a comminuted human fibula fracture fixation model, carbon fiber implants exhibited multiple pre-peak failures at significantly lower angles than the first failure for the stainless steel implants, with some delamination of composite layers and brittle catastrophic failure rather than plastic deformation. CLINICAL RELEVANCE: The torsional failure properties of carbon fiber composite one-third tubular plates determined in this independent study provide novel in vitro data for this alternative implant material.

Biomechanical evaluation of periprosthetic refractures following distal femur locking plate fixation.

INTRODUCTION: Distal femur fractures proximal to total knee femoral component constitutes the most prevalent type of periprosthetic fracture, and plate fixation treatment is associated with a 7.7% incidence of refracture proximal to the plate. The primary objective of this study was to compare proximal fixation techniques of a periprosthetic distal femur fracture plate in an osteoporotic bone model. The secondary objective was to determine the subsequent periprosthetic plate fracture pattern and/or complexity associated with each proximal plate fixation configuration. MATERIALS AND METHODS: A segmental defect was created in 21 synthetic osteoporotic adult femurs 6 cm proximal to the distal femur and all specimens were stabilised with a 246 mm locking femur plate. Fixation in the most proximal hole was varied by use of either a cerclage cable, unicortical locking screw, or a bicortical locking screw. Specimens were tested to failure in simultaneous eccentric compression and torsion. RESULTS: Proximal cerclage fixation demonstrated higher mean maximum axial force at failure (4142.67±178.71 N, p<0.001), stiffness (443.8±61.64 N/mm), and maximum torque (20.9±0.93 N m, p<0.001). Unicortical and bicortical screw refractures occurred at the screw, cerclage wire refractures occurred at the first proximal screw distal to the cerclage. CONCLUSIONS: In periprosthetic distal femur fracture locking plate fixation, proximal hole stabilization with a cerclage wire tolerates significantly higher failure forces while distributing forces distal to the area within the plate fixation. Cerclage wiring may be an option in distal femur periprosthetic fractures to alleviate stress risers in vulnerable bone.

Ultrasound for Infants at Risk for Developmental Dysplasia of the Hip.

The best screening method for developmental dysplasia of the hip is controversial. Ultrasonography is sensitive, but cost-effectiveness may limit its use. This study assessed whether ultrasound screening would increase in effectiveness if targeted toward infants with established risk factors for developmental dysplasia of the hip and normal findings on physical examination. All ultrasound scans performed at the authors' institution from January 2007 through January 2011 to screen for developmental dysplasia of the hip were reviewed. Infants with risk factors for developmental dysplasia of the hip and normal findings on physical examination by orthopedic faculty or a pediatrician were selected. Of the 530 cases that were reviewed, 217 had risk factors for developmental dysplasia of the hip and normal findings on physical examination. Mean age of the 217 selected patients was 6.9 weeks. Of the patients, 83% were female, 77% had breech presentation, 30% were firstborn children, 13% had intrauterine packaging abnormalities, and 3% had a family history of developmental dysplasia of the hip. Of the 217 infants, 44 had 1 risk factor, 121 had 2 risk factors, 46 had 3 risk factors, and 6 had 4 risk factors. Dynamic ultrasound evaluation showed instability in 17 patients, for a 7.8% incidence of developmental dysplasia of the hip. All 17 patients were treated with a Pavlik harness. The results suggested that selective ultrasound screening may be effective in infants with risk factors and normal findings on physical examination. Selective ultrasound screening changed treatment management in almost 8% of patients and clinical follow-up in 6.5%. Analysis of the cost-effectiveness of screening is needed.

Allograft Reconstruction of the Lisfranc Ligament.

UNLABELLED: For Lisfranc injuries, screw fixation of the medial and middle columns is currently the standard of treatment. The purpose of this study was to biomechanically evaluate the use of allograft for a severed Lisfranc ligament compared to standard screw fixation and the intact condition. Six pairs of fresh-frozen cadaveric lower extremities were prepared with reflective marker arrays and cyclically loaded to simulate partial weight bearing under 4 sequential testing conditions: (1) intact ligament, (2) disrupted ligament, (3) tendon allograft reconstructed ligament, and (4) rigid screw fixation. The relative displacement between the medial cuneiform and the second metatarsal was assessed via motion analysis. A mixed model analysis of variance was used to determine the significance (α = .05) of displacement differences. Mean displacements and 95% confidence intervals for each condition were as follows: (1) intact 9.1 (7.1-11.2) mm, (2) cut ligament 9.4 (7.4-11.5) mm, (3) allograft fixation 8.8 (6.8-10.9) mm, and (4) screw fixation 8.2 (6.2-10.3) mm. There were no significant differences among the specimens according to condition. Allograft fixation provided adequate strength and stability and did not differ significantly compared to intact or screw fixation. LEVELS OF EVIDENCE: Level V: Bench testing.

Gravity versus manual external rotation stress view in evaluating ankle stability: a prospective study.

BACKGROUND: The purpose of this prospective study was to determine whether gravity versus manual external rotation stress testing effectively detects widening of the medial clear space in isolated ankle fractures when compared with the uninjured contralateral side. METHODS: Manual external rotation stress and gravity stress tests were performed on injured and uninjured ankles of ankle fracture patients in a clinic setting. Medial clear space measurements were recorded and differences between gravity and manual stress views were determined. RESULTS: Twenty consecutive patients with ankle injury were enrolled in the study. When compared with the uninjured side, gravity stress views showed a statistically significant (P = .017) increase in medial clear space widening (1.85 ± 1.07 mm) compared with manual stress view widening (1.35 ± 1.04 mm). CONCLUSIONS: This study suggests that gravity stress views are as effective as manual external rotation stress views in detecting medial clear space widening in isolated fibular fractures. LEVEL OF EVIDENCE: Diagnostic, Level II: Prospective, comparative trial.

Accuracy of fluoroscopy versus computer-assisted navigation for the placement of anterior cervical pedicle screws.

STUDY DESIGN: Randomized laboratory cadaver study. OBJECTIVE: The objective of this study was to determine the accuracy of anterior transpedicular screw placement in the cervical spine using conventional fluoroscopy versus computer-assisted navigation. SUMMARY OF BACKGROUND DATA: Traditionally, global cervical instability has required anterior and posterior fixation due to the superior biomechanical stability of circumferential constructs. Anterior transpedicular screws (ATPS) have recently been advocated as a single surgical approach. Current clinical publications report using fluoroscopic guidance for screw placement. Computer-assisted navigation (CAN) systems have demonstrated enhanced accuracy of pedicle screw placement at all spine levels but have not been assessed for ATPS. METHODS: The anterior vertebrae of 9 fresh frozen cadaver cervical spines were exposed, preserving the lateral and posterior soft tissue envelope. Nine practicing spine surgeons placed 2.0-mm titanium anterior transpecidular Kirschner wires into the C3-T1 pedicles bilaterally using fluoroscopy or CAN guidance. Specimens were imaged by computed tomography and virtual screws were overlaid on the K-wires. Targeting accuracy was compared between the 2 techniques in all planes using a 5-level grading scale. RESULTS: The percentage of acceptable screw placements for fluoroscopy and CAN was 42.6% and 66.7%, respectively (P = 0.012). Catastrophic screw placement (grade 3 or 4) was 33.3% for fluoroscopy and 16.7% for CAN. In the multivariable model, the accuracy rate was 67% lower for fluoroscopy than for CAN after controlling for other factors (odds ratio: 0.33, 95% confidence interval: 0.14-0.79). CONCLUSION: The accuracy of CAN-guided placement of K-wires for ATPS was superior to placement under fluoroscopic guidance, demonstrating statistically more acceptable screw placements and significantly less catastrophic virtual screws. However, malposition was still high, with potential for vertebral artery and neurological injury in a clinical setting. Further advancement in current ATPS techniques is warranted prior to widespread implementation in a patient setting. LEVEL OF EVIDENCE: N/A.